Thermostat having positive insulating liner

ABSTRACT

A thermal control or protector having a conductive casing with two bi-metal arms extending as cantilevers into the casing from the ends thereof. The bi-metal arms have insulating sleeves therearound and a continuous insulating liner is provided that extends the length of the casing adjacent the wall thereof and protrudes beyond the ends of the casing for positive insulation thereof.

United States Patent [19] Wells ]March 20, 1973 [54] THERMOSTAT HAVING POSITIVE INSULATING LINER [76] Inventor: Alton R. Wells, 4573 W. Tradewinds Avenue, Lauderdale-by-the- Sea, Fla.

[22] Filed: Aug.3l,l97l

[2]] Appl. No.: 176,661

[52] US. Cl. ..337/ll2, 337/370, 337/380 [51] Int. Cl. ..H0lh 45/02 [58] Field of Search ..337/1 12, 370, 372, 380

[56] References Cited UNITED STATES PATENTS 2/1952 Dales ..337/37O 7/1946 Kearsley ..337/380X 3,012,122 12/196] Clelland ..337/380 2,320,8ll 6/1943 Cook ....337/38O X 3,609,620 9/1971 Lee ..337/1l2 X Primary Examirier-George Harris Assistant Examiner-F. E. Bell Attorney-Albert H. Oldham et al.

[57] ABSTRACT A thermal control or protector having a conductive casing with two bi-metal arms extending as cantilevers into the casing from the ends thereof. The bi-metal arms have insulating sleeves therearound and a continuous insulating liner is provided that extends the length of the casing adjacent the wall thereof and protrudes beyond the ends of the casing for positive insulation thereof.

5 Claims, 4 Drawing Figures PATENTEBHAR20I975 FIG.

FIG.4

ATTORNEYS.

THERMOSTAT HAVING POSITIVE INSULATING LINER v The present invention in general relates to motor protectors, thermostats and similar thermo-protectors for use in electric motors or in other articles, as desired.

BACKGROUND OF INVENTION Heretofore there have been many different types of thermostats provided and representative patents in this field include US. Pat. Nos. 2,586,309 and 2,497,397 that show a typical double end" thermostat as is in wide use today. However, these thermostats are expected to have very long and safe product control lives, and in some instances a contact may drop off of the arm in the thermostat or other device, or any insulation layer on the inner wall of the thermostat may chip, have weak spots therein, or otherwise not provide a completely effective continuous insulating liner in the metal casing.

The general object of the present invention is to provide an improved thermal protector having a continuous insulating liner or sleeve extending the length thereof and beyond the ends of a metal casing forming the carrier of the thermal protector assembly; and to provide a slow cycle motor protector.

Another object of the invention is to use a special multi-ply insulation liner in a thermal protector wherein adjacent plies in the insulating liner are oppositely wound and where the plies are made from an effective improved insulator, such as asbestos fiber.

Another object of the invention is to provide a relatively inexpensive, relatively small, easily assembled motor protector where a positive insulating liner is provided therein.

The foregoing and other objects and advantages of the invention will be made more apparent as the specification proceeds.

In the accompanying drawings:

FIG. 1 is a longitudinal section through a thermal protector embodying the principles of the invention;

FIG. 2 is an elevation, partially broken away, of the insulating liner of FIG. 1;

FIG. 3 is a vertical section taken on line 33 of FIG.

2; and

FIG. 4 is an elevation of the casing of FIG. 1 prior to assembly of the bi-metal arm members therein.

When referring to corresponding members shown in the drawings and referred to in the specification, corresponding numerals are used to facilitate comparison therebetween.

SUBJECT MATTER OF INVENTION A thermal control comprises a conductive metal casing initially having a pair of open ends, a bi-metal arm extends into the casing as a cantilever from each end thereof, and each bi-metal arm has a contact secured to its free end for operative engagement with a contact on the other arm for current transmission. A glass fiber or other insulating means is positioned around each of the arms at the ends of the casing, and a multi-ply spirally wound insulation sleeve is positioned within the casing adjacent the wall thereof and protruding from both ends of such casing. In the production of the thermal control, the end portions of the casing are pressed around the sleeve to engage said arms by the insulating sleeves provided and from end seals in the thermal protector.

With reference to the details shown in the structure of the drawings, a thermal protector or thermostat is indicated as a whole by the numeral 10. This thermostat or motor protector includes a metal tubular casing 12 of conventional design and which casing initially has two open ends.

.The thermostat includes, usually, a pair of bi-metal arms 14 and 16 each of which is secured adjacent one end of the casing to extend thereinto as a cantilever. Portions of the arms 14 and 16 protrude beyond the casing 12 for attachment of any desired terminals, connectors or equivalents thereto so that a circuit can be formed through the thermal protector 10. Each of these arms 14 and 16 has a contact 18 welded to the free end thereof with the two contacts 18 normally being adjacent each other so that on proper positioning of the arms 14 and 16, the contacts 18 will engage and close the circuit. However, when the temperature of the thermo-protector I0 is suitably elevated to a desired temperature controlled points, it is conventional practice for the arms 14 and 16 to be so made and positioned in the casing 12 as to more apart and open-the circuit formed between the contacts 18.

These arms 14 and 16 are positioned in the casing 12 by relatively conventional resin-fiber insulation sleeves, or equivalents 20 and 22 positioned therearound adjacent each end of the casing.

In the manufacturing of the thermal protector 10, as an important feature thereof, an insulation liner or sleeve 24 is associated with the casing 12 prior to assembly of the arms 14 and 16 and insulation means or liners 20 and 22 therein. This liner 24 is made from a multiply insulation structure and plies 24a and 24b are provided in the liner with the plies being helically wound in opposite directions as indicated in FIGS. 2 and 3 of the drawings and each ply, for example, may be about 1/32 inch thick. Preferably the liner 24 is made from highly purified asbestos fibers which are bonded together by polyvinyl acetate, or other temperature resistant resinous elastomer material whereby the asbestos fiber is rendered water resistant and has good insulation properties even at relatively high temperatures, such as up to 350 F. or more. The polyvinyl acetate resin is used in solution form as a binder material that is mixed with the asbestos fibers in quantities of about 10 to 17 percent by weight of the ply when forming a ply therefrom, which ply thereafter is processed to be wound into the liner 24 so that a two or more ply construction is obtained. By the use of the two plies in the liner 24, it ispossible to avoid any weak spots in the liner, and such continuous liner will prevent any short circuiting of the thermal protector 10 if one of the contacts 18 should fall off of its support arm, or if any por' tion of either arm moves to be adjacent the casing 12.

The insulation liner 24 also prevents any corona treeing effect between the contacts 18 and the case. Such effect is produced in thermal controls where silver from the coatings on the contacts 18 has been repeatedly splashed or dislodged from the contacts to deposit or bombard the case or any liner thereon. A full short does not result from such corona treeing, but a shock is obtainable from the case when such treeing occurs. It should also be noticed that the liner 24 protrudes beyond the casing at the ends thereof'so that if there are any burrs or other sharp metal edges formed on the casing, a good insulating medium is provided immediately thereadjacent to prevent any flow of current from the arms 14 and 16 to the casing. Normally this protrusion of the liner 24 from the ends of the casing may be about /8 inch. Also, such liner 24 aids in sealing the ends of the casing 12 against an oil, varnish, or other liquid immersion or penetration without any dip sealing means being required.

By the use of the improved liner means of the invention, the motor protector or thermal control has served efficiently and maintains high dielectric valves up to temperatures well beyond 350 F. and it will function under high amperage and voltages of 240 and 277 volts. Each of the plies of the liner 24 comprise a sheet of the asbestos fiber-resin material. A relatively small protector 10 can be used for many purposes. The liner 24 usually frictionally engages the wall of the casing 12.

In view of the foregoing, it is believed that a novel and improved thermal control has been provided and that the objects of the invention have been achieved.

The dual end thermostats may be calibrated and/or have its ends compressed or formed as in prior U.S. Pat. Nos. 2,497,397; 2,586,309 and 3,209,107.

While one complete embodiment of the invention has been disclosed herein, it will be appreciated that modification of this particular embodiment of the invention may be resorted to without departing from the scope of the invention.

What I claim is:

1. A thermostat, motor protector or the like thermal control comprising I a metal casing initially having a pair of-open ends,

a conductive arm extending into said casing as a cantilever from each end thereof and having a contact secured to its free end, one of said arms being responsive to temperature changes to change its position in said casing, w an insulating means positioned around each of said arms at the ends of said casing, and a multi-ply spiral wound insulation sleeve within said casing adjacent the wall thereof and protruding from both ends thereof, the end portions of said casing being deformed inwardly to engage said an insulating sleeve positioned around each of said' arms at the ends of said casing, and

a multi-ply opposing spiral wound insulation sleeve within said casing adjacent the wall thereof and protruding from both ends thereof, the end portions of said casing being compressed around said sleeves to engage said arms and form a seal therearound, said insulation sleeve made from a fire resistant material with adjacent plies bonded together by a temperature resistant material.

4. A thermal control as in claim 3 where said insulatio n sleeve has two plies therein with two plies being spirallywound in opposite directions, said plies being made from asbestos fiber.

5. A thermal control as in claim 4 where the temperature resistant resinous material is polyvinyl acetate. 

1. A thermostat, motor protector or the like thermal control comprising a metal casing initially having a pair of open ends, a conductive arm extending into said casing as a cantilever from each end thereof and having a contact secured to its free end, one of said arms being responsive to temperature changes to change its position in said casing, an insulating means positioned around each of said arms at the ends of said casing, and a multi-ply spiral wound insulation sleeve within said casing adjacent the wall thereof and protruding from both ends thereof, the end portions of said casing being deformed inwardly to engage said arms and form a seal therearound.
 2. A thermal control as in claim 1 wherein said insulation sleeve has at least two plies therein with the two plies being spirally wound in opposite directions.
 3. A thermostat, motor protector or the like thermal control comprising a tubular metal casing initially having a pair of open ends, a bi-metal arm extending into said casing as a cantilever from each end thereof and having a contact secured to its free end, an insulating sleeve positioned around each of said arms at the ends of said casing, and a multi-ply opposing spiral wound insulation sleeve within said casing adjacent the wall thereof and protruding from both ends thereof, the end portions of said casing being compressed around said sleeves to engage said arms and form a seal therearound, said insulation sleeve made from a fire resistant material with adjacent plies bonded together by a temperature resistant material.
 4. A thermal control as in claim 3 where said insulation sleeve has two plies therein with two plies being spirally wound in opposite directions, said plies being made from asbestos fiber.
 5. A thermal control as in claim 4 where the temperature resistant resinous material is polyvinyl acetate. 